The present invention relates to a material for one-piece intraocular lenses.
Intraocular lenses are composed of a lens body and a haptic. The intraocular lenses are mainly classified into one-piece intraocular lenses of which lens body is formed integrally with a haptic and three-piece intraocular lenses produced by assembling a lens body and a haptic which are manufactured separately from each other.
As the material of the one-piece intraocular lens, a hard-type material composed of a hard material such as polymethyl methacrylate, and a soft-type material composed of a soft material such as a silicone rubber not having water-absorptive property or poly(2-hydroxyethyl methacrylate) having water-absorptive property are known.
One-piece intraocular lenses composed of a hard-type material such as polymethyl methacrylate have some advantages that include excellent positioning in eyes, stability for visual acuity and biocompatibility and little degradation in human eyes. However the intraocular lenses have some disadvantages, which include that the lenses cannot be easily inserted into eyes on operation because the haptic has small flexibility, and that the haptic is easily broken during the implantation of the intraocular lens in eyes because its flexural strength is small.
Also, one-piece intraocular lenses composed of a soft-type material have some advantages that the one-piece intraocular lenses mechanically little damage the tissues of eyes even though the intraocular lenses are touched to a corneal endothelium or an iris during their insertion in eyes since the intraocular lenses are generally soft. However, their positioning is insufficient since the haptic is soft, and therefore, the intraocular lenses are easily slidden or defected and visual acuity is apt to be unstable.
Accordingly, as a one-piece intraocular lens dissolving the above-mentioned defects, an intraocular lens not having water-absorptive property and having suitable flexibility and excellent mechanical strength has been developed (Japanese Unexamined Patent Publication No. 97559/1987 and Japanese Unexamined Patent Publication No. 158949/1989).
The intraocular lenses described in the above-mentioned publications surely do not have water-absorptive property and have suitable flexibility and excellent mechanical strength, but it is difficult to polish its material to give an intraocular lens having a desired lens shape by means of conventional polishing methods. Therefore, the improvement of mechanical processability has been expected.
It is an object of the present invention to provide a material for one-piece intraocular lenses having a hard optical portion and a haptic having suitable elasticity.
It is another object of the present invention to provide a material for one-piece intraocular lenses having excellent cutting processabity as well as excellent positioning in eyes.
These and other objects of the present invention will become apparent from the description hereinafter.